Progressive Multifocal Leukoencephalopathy Initially Considered as Central Nervous System Involvement of Post-Transplant Lymphoproliferative Disorder: The Critical Role of Contrast Enhancement on Magnetic Resonance Imaging.

A 58-year-old allogeneic stem cell transplant recipient developed dizziness during chemotherapy for systemic post-transplant lymphoproliferative disorder. Brain magnetic resonance imaging (MRI) revealed multiple lesions on fluid-attenuated inversion recovery images; however, they lacked gadolinium contrast enhancement. Under the assumption of central nervous system post-transplant lymphoproliferative disorder (PTLD), we treated the patient with high-dose methotrexate without success. The absence of contrast enhancement on MRI and unresponsiveness to chemotherapy led us to suspect progressive multifocal leukoencephalopathy (PML). The presence of John Cunningham virus DNA in the cerebrospinal fluid led to a definitive diagnosis. Therefore, clinicians encountering patients with enhancement-lacking brain lesions during PTLD should consider PML.